1. Field of the Invention
The present invention relates to a silicon oxynitride film used in a semiconductor device and more particularly, to an improvement in the silicon oxynitride film to have high moisture resistance.
2. Description of the Related Art
A silicon nitride film has been used widely in a semiconductor device as a passivating overcoat film and as an inter-layer insulation film for a multi-layered wiring.
However, voids are created in the aluminum wiring due to a large stress of the silicon nitride film when the aluminum wiring on a silicon (Si) substrate is covered with the silicon nitride film and subjected to heat-treatment above 450.degree. C., as reported by J. T. Yue et al in "Stress Induced Voids in Aluminum Interconnects during IC Processing", 23rd annual proceedings reliability physics 1985 pp. 126.about.137. When the width of the aluminum wiring layer is sufficiently large, voids do not completely cut away the aluminum wiring layer. However, the problem becomes serious if the width is reduced to 2 .mu.m or less. In that case, the aluminum wiring may be cut away by the voids.
It has been proposed to use a silicon oxynitride film instead of the silicon nitride film to mitigate the stress, in "Silicon Oxynitride Films from the NO-NH.sub.3 -SiH.sub.4 Reaction", Journal of Electrochemical Soc., Vol. 120, No. 3, 1973, pp. 446.about.453. The composition of the silicon oxynitride film disclosed in this article is a compound of SiO.sub.2 and Si.sub.3 N.sub.4, that is, (SiO.sub.2).sub.x (Si.sub.3 N.sub.4).sub.1-x (where 0&lt;x&lt;1).
The present inventors have found, however, that the proposed composition of the silicon oxynitride film is disadvantageous in having a lower moisture resistance than that of a Si.sub.3 N.sub.4 film. The (SiO.sub.2).sub.x (Si.sub.3 N.sub.4).sub.1-x film cannot be used as a passivation overcoat film and an inter-layer insulation film for a semiconductor device. The U.S. Pat. No. 4,097,889 discloses the use of the silicon oxynitride film as the passivation film of semiconductor devices, stating about the composition of the silicon oxynitride film, however, only that a chemical compound has the formula Si.sub.w N.sub.x H.sub.y O.sub.z wherein w, x, y and z are integers other than zero. It does not teach the composition of silicon oxynitride which does not create the voids in the aluminum wiring and has high moisture resistance.